U.S. patent application number 09/727940 was filed with the patent office on 2002-06-13 for method of making opto-electronic devices using sacrificial devices.
Invention is credited to Dudoff, Gregory K., Trezza, John A..
Application Number | 20020072138 09/727940 |
Document ID | / |
Family ID | 22611725 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020072138 |
Kind Code |
A1 |
Trezza, John A. ; et
al. |
June 13, 2002 |
Method of making opto-electronic devices using sacrificial
devices
Abstract
A method for making optoelectronic devices with interdigitated
arrays of photonic devices is disclosed wherein an array of first
type photonic devices and sacrificial device(s) is hybridized to a
driver circuitry substrate, the sacrificial devices are removed,
and an array of second type photonic devices is hybridized into the
spaces left by removal of the sacrificial devices.
Inventors: |
Trezza, John A.; (Nashua,
NH) ; Dudoff, Gregory K.; (Amherst, NH) |
Correspondence
Address: |
MAINE & ASMUS
100 MAIN STREET - SUITE 3
PO BOX 3445
NASHUA
NH
03061-3445
US
|
Family ID: |
22611725 |
Appl. No.: |
09/727940 |
Filed: |
December 1, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60168493 |
Dec 2, 1999 |
|
|
|
Current U.S.
Class: |
438/23 ; 438/25;
438/26; 438/455; 438/458 |
Current CPC
Class: |
H01S 5/0262 20130101;
H01S 5/0217 20130101; H01S 5/0234 20210101; H01L 2224/95 20130101;
H01L 2221/68363 20130101; H01S 5/4025 20130101; H01S 5/0237
20210101; H01L 31/167 20130101; H01S 5/0215 20130101; G02B 6/4246
20130101; H01L 2224/81 20130101 |
Class at
Publication: |
438/23 ; 438/455;
438/458; 438/25; 438/26 |
International
Class: |
H01L 021/00; H01L
021/30; H01L 021/46 |
Claims
What is claimed is:
1. A method of making a hybrid optoelectronic device, the method
comprising: hybridizing a first substrate and a second substrate,
said second substrate including at least one first type optical
device and at least one sacrificial device; introducing a first
flowable hardenable material to join said first and second
substrates; curing said first flowable hardenable material;
removing said second substrate; removing said at least one
sacrificial device; hybridizing said first substrate and a third
substrate, said third substrate including at least one second type
optical device; introducing a second flowable hardenable material
to join said first and third substrates; curing said second
flowable hardenable material; and removing said third
substrate.
2. The method of claim 1 wherein the first substrate is a silicon
substrate containing integrated circuitry for a plurality of
optical devices.
3. The method of claim 1 wherein the second and third substrates
are chosen from the group of III-V materials, sapphire, and organic
polymers.
4. The method of claim 3 wherein the second and third substrates
are GaAs.
5. The method of claim 1 wherein the at least one first type
optical device is an emitter.
6. The method of claim 1 wherein the at least one second type
optical device is a detector.
7. The method of claim 1 wherein the at least one second type
optical device is a modulator.
8. The method of claim 7 wherein the modulator is selected from the
group of transmissive, reflective and absorptive modulators.
9. The method of claim 7 wherein the modulator operates to modulate
the amplitude of a received signal.
10. The method of claim 7 wherein the modulator operates to
modulate the wavelength of a received signal.
11. The method of claim 7 wherein the modulator operates to
modulate the phase of a received signal.
12. The method of claim 1 wherein the first and second flowable
hardenable materials are curable epoxy resins.
13. The method of claim 6 further comprising the step of applying
an anti-reflective coating to the receiver.
Description
RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Patent Application Serial No. 60/168,493, filed Dec. 2, 1999.
FIELD OF THE INVENTION
[0002] This invention relates to optical communication systems and
more particularly to a process for making optical transceiver
arrays.
BACKGROUND OF INVENTION
[0003] Optical couplers are now used to communicate optical signals
over short and long distances between, for example, two computers,
two circuit boards in one computer, and even two different chips on
the same circuit board.
[0004] Integrated circuit technology that enables bi-directional,
high-speed optical rather than electrical interconnections has been
developed. This technology allows laser emitters and detectors to
be integrated onto a semiconductor substrate, making electrical
connection with electronic circuitry previously built on that
substrate.
[0005] Thus, optical rather than electrical communications between
electronic devices is accomplished. An optical transmitter-receiver
module, or optoelectronic device, typically includes both light
emitting devices such as vertical cavity surface emitting lasers
(VCSELs) and light detecting devices such as photodiodes. Such a
module more typically may include separate chips, or the VCSELs and
the photodiodes may be grown on the same substrate. See U.S. Pat.
No. 5,978,401 incorporated herein by this reference.
[0006] Driver-receiver circuit modules, typically in the form of
ASIC chips, include driver circuitry which receives electrical
signals from an electronic device and drives the VCSELs
accordingly. The ASIC chips also include receiver circuitry for
receiving signals from the photodiodes and processes those
electrical signals providing an appropriate output to the
associated electronic device.
[0007] The combination of the VCSELs and the photodiodes and the
ASIC circuitry is typically called an optical transceiver. One way
to hybridize the VCSELs and the photodiodes and the ASIC receiver
circuitry is by flip-chip bonding. See U.S. Pat. No. 5,858,814,
incorporated herein by this reference.
[0008] These different types of photonic devices, e.g., emitters
and detectors, however, have very different epitaxial layer
constructions and physical dimensions, and it is not economically
feasible to grow such dissimilar devices on the same substrate.
Therefore, separate growth steps must be performed for each device
type. This method, in turn, restricts the number of different
device types integrated onto the same silicon substrate.
SUMMARY OF THE INVENTION
[0009] It is therefore an object of this invention to provide a
method for making a hybrid optoelectronic device with multiple
types of photonic devices, such as emitters and detectors,
integrated on the same silicon substrate.
[0010] It is a further object of this invention to provide a method
of making a hybrid optoelectronic device with multiple types of
photonic devices interdigitated on the same silicon substrate.
[0011] This invention results from the realization that an
interdigitated array of photonic devices with at least two
different photonic devices of different physical and epitaxial
layer construction, can be produced with good electrical and
mechanical interconnections by using a multistep hybridization
process including the use of sacrificial, or dummy, devices in at
least a first array of photonic devices. The sacrificial devices
are removed before a second array of photonic devices is hydridized
with the first array.
[0012] The present invention provides a method of making a hybrid
optoelectronic device. The primary steps are hybridizing a first
substrate and a second substrate, the second substrate including at
least one first optical device and at least one sacrificial device
and introducing a first flowable hardenable material to join the
first and second substrates. The first flowable hardenable material
is then cured. The second substrate is then removed as is the at
least one sacrificial device. The method also includes hybridizing
the first substrate and a third substrate, the third substrate
including at least one second optical device; introducing a second
flowable hardenable material to join the first and third
substrates; curing the second flowable hardenable material; and
removing the third substrate.
[0013] The first substrate material may be silicon. The second and
third substrate materials may be GaAs. The flowable hardenable
materials may be curable epoxy resins.
[0014] The photonic devices may be emitters, transmitters and/or
modulators. Modulators may be reflective, transmissive or
absorptive and may modulate a received signal based on amplitude,
wavelength or phase.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Other objects, features and advantages will occur to those
skilled in the art from the following description of a preferred
embodiment and the accompanying drawings, in which:
[0016] FIG. 1 is a cross-sectional view of a silicon substrate and
a first GaAs substrate, with first optical and sacrificial devices
thereon, before hybridization.
[0017] FIG. 2 is a cross-sectional view of the substrates of FIG. 1
after hybridization.
[0018] FIG. 3 is a cross-sectional view of the hybridized
substrates of FIG. 2 after a first flowable hardenable material has
been introduced.
[0019] FIG. 4 is a cross-sectional view of the device of FIG. 3
after mechanical lapping to remove most of the first GaAs
substrate.
[0020] FIG. 5 is a cross-sectional view of the device of FIG. 4
after etching to remove the remainder of the first GaAs
substrate.
[0021] FIG. 6 is a cross-sectional view of the device of FIG. 5
after removal of the etch stop layer.
[0022] FIG. 7 is a cross-sectional view of the device of FIG. 6
with a process mask applied thereto.
[0023] FIG. 8 is a cross-sectional view of the device of FIG. 7
after removal of the sacrificial devices.
[0024] FIG. 9 is a cross-sectional view of the device of FIG. 8
with a second GaAs substrate, with second optical devices thereon,
before hybridization.
[0025] FIG. 10 is a cross-sectional view after hybridization of the
second GaAs substrate.
[0026] FIG. 11 is a cross-sectional view of the device of FIG. 10
after introduction of a second flowable hardenable material.
[0027] FIG. 12 is a cross-sectional view of the device of FIG. 11
after removal of most of the second GaAs substrate.
[0028] FIG. 13 is a cross-sectional view of the device of FIG. 12
after removal of the remainder of the second GaAs substrate.
[0029] FIG. 14 is a cross-sectional view of the device of FIG. 13
with a process mask applied.
[0030] FIG. 15 is a cross-sectional view of the device of FIG. 14
after removal of epoxy from the first optical devices and the
second etch stop layer over the second optical devices.
DISCLOSURE OF THE PREFERRED EMBODIMENT
[0031] As shown in FIG. 1, silicon substrate 10, with driver
circuitry (not shown), has metal bonding pads 12 and solder bumps
14 formed on one surface thereof. GaAs substrate 20 has emitters 22
and sacrificial devices 24 grown epitaxially on one surface
thereof. Emitters 22 and sacrificial devices 24 also have solder
bumps 26 formed thereon which align with solder bumps 14 on silicon
substrate 10. Emitters 22 are identical, having been grown on the
same GaAs substrate with the same epitaxial layer construction.
Similarly, sacrificial devices 24 have the same epitaxial layer
construction.
[0032] While substrate 20 is preferably GaAs, it may be of any
material compatible with the growth of epitaxial layers of III-V
materials that support light emission, such as GaAs or InP. This
includes II-V materials, sapphire and organic polymers.
[0033] The emitter attachment step is performed by pressing GaAs
substrate 20 and silicon substrate 10 together as shown in FIG. 2.
During this process, the surfaces of solder bumps 14 interlock with
the corresponding solder bumps 26, thereby developing a low
electrical resistance, mechanically stable connection in each
aligned solder bump pair. This process is also referred to as
"hybridizing."
[0034] After the pressing step is complete, a flowable hardenable
material 30 (FIG. 3), such as an epoxy resin, is introduced into
the spaces between and around emitters 22 and sacrificial devices
24. Flowable hardenable material 30 provides physical stability for
emitters 22 during the subsequent processing steps. Once flowable
hardenable material 30 is introduced, it is cured as appropriate,
such as exposure to UV light if a UV-curable epoxy resin is
used.
[0035] Next, the bulk of substrate 20 is removed using a mechanical
lapping process or other suitable mechanical process, as shown in
FIG. 4. Preferably, the thickness of substrate 20 remaining after
the mechanical lapping process is complete is in the range of 10 to
50 microns. The mechanical lapping process also leaves polished
epoxy standoff 40, which can be used to attach faceplates or
microlens to the finished optical transceiver device.
[0036] A selective dry chemical etch is then used to remove the
rest of substrate 20 as shown in FIG. 5. Various dry etch
formulations enable selective removal of semiconductor material.
For example, to remove a GaAs substrate, a dry etch composition
consisting of SiCl.sub.4/SF.sub.6 can be used. The dry etch process
is complete when etch stop layer 50 is reached. Etch stop layer 50
is composed of material which is not susceptible to dry etching by
the dry etch composition used to remove substrate 20.
[0037] A separate dry etch step is used to remove etch stop 50, as
shown in FIG. 6. Again, the dry etch composition selected removes
only etch stop layer 50, leaving GaAs layer 60 exposed.
[0038] As shown in FIG. 7, process mask 70 is placed over the top
surface of the devices. Process mask 70 protects emitters 22 but
has openings 72 that expose sacrificial devices 24. Openings 72
allow a selective wet chemical etch to remove sacrificial devices
24. This wet chemical etch does not remove solder bumps 26 or epoxy
30, as shown in FIG. 8. Typical compositions for the wet chemical
etch would include Br.sub.2 and HBr.
[0039] FIG. 9 shows GaAs substrate 90, with photonic devices 92
grown thereupon. Photonic devices 92 are typically detectors or
photodiodes. These detectors are typically shorter in height than
emitters 22. To accommodate for this height difference, solder
bumps 94, in combination with solder bumps 14 and 26 remaining
after sacrificial devices 24 were removed, are provided with the
appropriate height. Substrate 90 is pressed together with substrate
10 such that solder bumps 94 interlock with solder bumps 14 and 26
and is intended to form a good electrical and mechanical contact,
as shown in FIG. 10.
[0040] Flowable hardenable material 100, FIG. 11, is then
introduced in the spaces between and around detectors 92 and
flowable hardenable material 30. Flowable hardenable materials 30
and 100 may be the same composition or may differ in composition.
Flowable hardenable material 100 is then cured by appropriate means
once it is introduced, as for example, by UV light if a UV-curable
epoxy is used. After curing, flowable hardenable material 100
provides mechanical stability for detectors 92.
[0041] A mechanical process, such as lapping, is used to reduce the
thickness of substrate 90 to a range of about 30 to 50 microns, as
shown in FIG. 12. A selective dry chemical etch is then used to
remove the rest of substrate 90. Etch stop layer 110, FIG. 13,
prevents the dry chemical etch advancing beyond that layer.
[0042] A second process mask 120, shown in FIG. 14, is placed over
the integrated device to protect detectors 92 during a dry chemical
etch which removes epoxy 100 and etch stop 110 from above detectors
92.
[0043] FIG. 15 illustrates the finished device 120. Anti-reflection
coating 122 may be optionally applied to detectors 92 to allow
light to enter the detector with minimum loss. This may help
improve performance in some systems.
[0044] While the process has been described with respect to an
interdigitated array of emitters and detectors in a hybrid Si/GaAs
chip technology, it is possible to use this method for any number
of types of photonic devices in other hybrid material chip
technologies. For example, photonic devices such as modulators
could be used. These modulators may be transmissive, reflective or
absorptive and may modulate the amplitude, wavelength or phase of
the received signal. Also, although the process has been described
with respect to interdigitation of two different optical type
devices, namely emitters and detectors, the process is expandable
to three or more different types of optical devices in the same
optoelectronic device.
[0045] The sacrificial devices may also be of exactly the same
structure as the photonic devices. The photolithographic masking
step will serve to protect the photonic devices to remain as part
of the optoelectronic device while allowing the sacrificial devices
to be removed.
[0046] Thus, although specific features of the invention are shown
in some drawings and not in others, this is for convenience only as
each feature may be combined with any or all of the other features
in accordance with the invention. The words "including",
"comprising", "having", and "with" as used herein are to be
interpreted broadly and comprehensively and are not limited to any
physical interconnection. Moreover, any embodiments disclosed in
the subject application are not to be taken as the only possible
embodiments.
[0047] Moreover, other embodiments will occur to those skilled in
the art and are within the following claims:
* * * * *